1. Field of the Invention
This invention relates to a method for stabilizing a silver halide photographic material in the dry state.
2. Description of the Prior Art
Silver halide photographic materials in general are fixed by dissolving the silver halide with a fixation bath after the formation of an image, and then removing the dissolved silver complex ion by washing with water.
A method for stabilizing a silver halide photographic material intended for shortening the processing time is known. The method comprises converting the silver halide to a silver complex compound devoid of photosensitivity after the formation of an image, without performing washing with water. Specifically, this method is performed by dipping a silver halide photographic material having an image formed thereon in an aqueous solution containing magnesium thiosulfate or thiourea as stabilizer, and then drying the material (see Photographic Chemistry, Vol. 1, page 158, Section 149, Fountain Press, 1958). Since, however, this processing is a wet processing by which the photographic material is passed through an aqueous processing bath the photographic material must be dried in the final step. The presence of the drying step is a great defect from the viewpoint of shortening the treating time. Furthermore, the use of a treating liquid causes contamination of things around it or requires control with respect to the preparation or exchanging of the processing liquid. Accordingly, it would be very significant to provide a new dry stabilizing method.
Methods are known in which an image is formed on a silver halide photographic material by a dry treatment such as print-out, thermo-development or photo-development in an attempt to remove the various defects of the wet processing. However, in these methods also, the recorded images cannot be preserved unless they are stabilized, that is to say, unless the discoloration of the non-image area by light is prevented when the processed photographic material is allowed to stand in a bright room. In other words, a method of dry stabilization is required.
One such dry stabilization method is disclosed in U.S. Pat. No. 3,447,927. This method is one in which dry stabilization is carried out imagewise, and is quite different from the dry stabilization method in accordance with this invention. If stabilization is only carried out imagewise, the density of the image area changes progressively when the recorded photographic material stands in a bright place.
In contrast, the dry stabilization method of this invention permits stabilization of both the colored area and the non-colored area of the image at the same time; in other words, it inhibits print-out. Accordingly, the dry stabilization method of this invention is complete in contrast to the dry stabilization method disclosed in U.S. Pat. No. 3,447,927, and this method brings about the same effect in the dry state as the conventional wet stabilization method disclosed in the above-cited Photographic Chemistry.
Another conventional dry stabilization method is disclosed in U.S. Pat. No. 3,615,510. This method comprises stabilizing silver halide using a compound selected from the group consisting of organic sulfonium halides, organic sulfoxonium halides, organic ammonium halides, organic phosphonium halides, organic boronium halides, organic siliconium halides, and mixtures of these materials. According to the disclosure of this United States Patent, these compounds are complex salt forming agents for the silver halide, and cations of these compounds play an important role in the formation of complex salts. In order to stabilize the silver halide by dry processing, an image stabilizing layer must be provided by adding such a compound to a low-melting non-aqueous solvent and a polymerizable binder in which the melted solvent can be diffused, and coating the mixture on the silver halide emulsion layer. When the photographic material so produced is heated, the solvent melts and the complex salt forming agent diffuses into the emulsion layer and reacts with the silver halide to thereby stabilize the photographic material.
In order to achieve this object, the manufacturing of the photographic material requires an additional step of providing the image stabilizing layer adjacent the photographic layer. As an alternative procedure, the complex salt forming agent is coated on a developing web, and the photographic material is heated while in contact with it. However, it is advantageous to add the complex forming agent directly to the emulsion before the coating of the stabilizer rather than to provide the stabilizing layer (complex salt forming agent).
When the compound disclosed in U.S. Pat. No. 3,615,510 is used, the addition of the stabilizer to the emulsion is conveniently effected by coating an aqueous solution of the stabilizer at room temperature or at a lower temperature. It is difficult, however, to include the stabilizer in the solidified emulsion layer in the amount required for stabilization. Thus, it is most preferable to add the stabilizer to the emulsion in the molten state, that is, to the emulsion which has been heated to a temperature higher than room temperature to disperse it fully and uniformly into the emulsion, and then coat the mixture on a support.
Furthermore, the amount of the complex salt forming agent should be that required to convert all of the silver halide to an onium halide-silver halide complex salt (a stabilizing amount). Theoretically at least one mole of an onium salt is required per 3 moles of the silver halide, and in actual operation, the onium salt should be used in an amount at least 4 times as large as this theoretical value (at least 4 moles of the onium salt per 3 moles of the silver halide). This is not desirable from the viewpoint of cost.
It is an object of this invention to provide a dry stabilization method for a silver halide photographic material using a small amount of a stabilizer.
Another object of this invention is to provide a dry stabilization method for a silver halide photographic material in which the emulsion layer contains a stabilizer.
Still another object of this invention is to provide a dry stabilizing method which does not require a stabilization promotor such as a non-aqueous solvent.